1. Field of the Invention
The present invention relates to forced air furnaces and in particular to forced air furnaces of the type used in residential installations.
2. Related Art
Conventional hot air furnaces such as those commonly installed to heat one- or two-family homes operate by forcing the air to be heated along a primary airflow path through a heat exchange chamber within which is disposed a heat exchanger. A blower forces the air past the coils of the heat exchanger to heat the air by indirect heat exchange, and thence through outlet ducts into the space to be heated. A system of return ducts serves to conduct return air from the heated space back to the blower for recirculation through the heat exchanger and reheating. The heat exchanger conventionally is heated by combustion product gases which are generated by a burner assembly positioned at the inlet to the heat exchanger coils and introduced into the heat exchanger. Combustion air may be provided to the burners by ambient air, for which purpose inlet ducts may be provided in the basement, attic or other enclosure or area in which the furnace is located. Fuel is supplied to the burners via a suitable fuel conduit, e.g., a pipe to conduct natural gas to the burners. The combustion product gases, after giving up heat to the primary air through the walls of the heat exchanger coils, are typically withdrawn from the heat exchanger outlet by a draft inducer blower and flowed via vent ducts to a chimney for discharge to the atmosphere. Accordingly, such furnaces must be coupled to outlet ducting to direct the heated air to the space (rooms) to be heated, to return ducting to direct air from the heated space back to the furnace for heating, to vent ducting to direct the cooled combustion product gases from the heat exchanger outlet to the chimney, to a fuel supply pipe, and sometimes to a combustion air supply duct.
Conventionally, manufacturers have carried a line of several differently configured furnaces in order to accommodate different types of installations. The space available for a furnace installation is usually limited and this and other considerations may dictate the use of any one of a number of installation configurations. To illustrate, the furnace may be installed as an upflow furnace, in which the primary air blower is below the heat exchanger and the primary airflow is directed upwardly from the furnace, as a down flow furnace, in which the primary air blower is above the heat exchanger and the primary airflow is directed downwardly from the furnace, or as a horizontal flow furnace, in which the primary air blower and heat exchanger are side by side and the primary airflow from the furnace is horizontally directed. Design and space considerations may require the outlet, return and vent ducting to be oriented in a particular direction relative to the furnace. For both upflow and downflow furnaces it is normally desired to direct the vent discharge, that is, the flue gases exiting from the heat exchanger, upwardly from the furnace to vent ducting. For horizontal primary airflow furnaces it may be desired to direct the flue gases either leftwardly or rightwardly from the furnace, thence to upwardly directed vent ducting. These factors have in the past required that different furnace designs be kept in inventory in order to accommodate different installation requirements, i.e., different combinations of horizontal, upwards or downwards primary airflow direction and horizontal and upwards vent discharge flow directions. Such choices may be dictated by the physical installation space within which the furnace is disposed, the design of the ducting which must be attached to the furnace, and other such considerations. For example, the building in which the furnace is to be installed may have pre-existing ducting in place so that the furnace must be configured in a manner which permits utilization of existing duct work, and/or limited space available for the furnace. Available space limitations may be severe, e.g., when the furnace is installed in a low-ceiling basement, in the rafters beneath a low roof attic, or within a small utility closet enclosure, etc.
Some attempts have been made in the prior art to enhance the versatility of furnaces with regard to installation. For example, U.S. Pat. No. 4,899,726 to Waterman, dated Feb. 13, 1990, discloses an inducer outlet elbow which directs combustion products from the inducer outlet to a flue. As seen in FIG. 2, where the inducer outlet is disposed upwardly, the inducer elbow 22 changes the direction of flow of the combustion products to the right about 90.degree. from the direction of the inducer outlet. As discussed in column 4, lines 6-16, the elbow can be reversed on the inducer outlet to discharge the combustion products to the left.
U.S. Pat. No. 4,739,746 to Tomlinson, dated Apr. 26, 1988, discloses a heat exchanger for a furnace in which the direction of flow of combustion products through the heat exchanger relative to the flow of heated air in the primary airflow path through the heat exchange chamber may be reversed by inverting the heat exchanger elements. However, as is evident from a comparison of FIGS. 1 and 2 and the related text of column 4, lines 20-36, the inversion of the heat exchanger elements requires a dismantling and reinstallation of the burner assembly and the inducer assembly. In particular, as illustrated in FIGS. 1 and 2, the inducer outlet is disposed upwardly regardless of which heat exchanger configuration is used.